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\noindent{\bf Octav ONICESCU}\\
b. 20 August 1892 - d. 19 August 1983
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\noindent{\bf Summary.} Onicescu is principally known as
co-founder,together with Gheorghe Mihoc (1906-1981), of the Romanian
school of probability
as well as for his contributions to mechanics.
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Octav Onicescu was born in 1892 in Boto\c{s}ani, a town
of North Moldavia, into the family of a small landowner. After his
baccalaureat in 1911 he became a student of the University of
Bucharest. He took a degree in mathematics in 1913, becoming then
a teacher of mathematics at the reputed military gymnasium of Dealu
Monastery, near T\^{a}govi\c{s}te. After having been called for
military duty in the period 1916-1918, he left for Rome in 1919,
where in the feverish atmosphere generated by the Einstein theory
of general relativity, he started a scientific activity which was
to last for more than six decades. Guided by Tullio Levi-Civita
(1873-1941) at the University of Rome, Onicescu has already
defended his doctoral thesis {\it Sopra gli spazi einsteinieni a
gruppi di transformazioni} by June 1920. In the autumn of 1920
Onicescu left for Paris, where he attended the lectures given at
the Sorbonne by \'Emile Picard and \'Elie Cartan,
and delivered papers on absolute differential calculus
at the seminar led by Jacques Hadamard (1865-1963) at the Coll\`ege
de France.
Onicescu's interest in probability theory and mechanics originated
in his Italo-French period of studies. He got interested in
probability by attending a seminar led by Francesco Paolo Cantelli
(1875-1966) and his interest in mechanics stemmed from Cartan's
lectures on integral invariants.
Back in Bucharest, Onicescu began (1922) a forty-year long
university career of a great variety. In 1924 he started teaching
the first university course on probability theory in Romania, an
enterprise which went on without interruption until his retirement
in 1962. In 1938 Onicescu was tenured as full professor at the
chair of algebra of the Mathematics Section of the Faculty of
Sciences of the University of Bucharest, where he played a dominant
part in modernizing the teaching of the subject. After the
reorganization (1948) of higher education in Romania, Onicescu was
until his retirement the head of the chair of probability theory of
the Faculty of Mathematics and Physics of the University of
Bucharest. He organized and guided (even after retiring) the
scientific seminars of the chair, which together with the expected
chapters from probability and stochastic processes were dedicated
to the most varied topics such as functional analysis, Lie groups
and algebras, game theory, and mathematical logic. In the same
period Onicescu was also the head of the Probability Theory Section
of the newly (1949) founded Institute of Mathematics of the
Romanian Academy.
On the organizational side, Onicescu founded in 1931, under the
auspices of the University of Bucharest, the School of Statistics,
which was to become, ten years later, the Institute of Statistics,
Actuarial Science and Computation of the University of Bucharest.
The creation of this school was an answer to the lack of
specialists in statistics, pointed out by the 1930 general
population census in Romania. The students of the institute were
university graduates and the duration of instruction was one year.
The institute, dismantled in 1947, should be considered as one of
the first institutions of postgraduate studies in statistics and
computation in the world.
At the international level, Onicescu was one of the initiators of
the Balkan Union of Mathematicians (founded 1934), which assembles
the representatives of mathematicians from Albania, Bulgaria,
Greece, former Yugoslavia, Romania and Turkey. The setting up in
1968 of the International Centre for Mechanical Sciences in Udine
(Italy) owes much to the scientific prestige of Onicescu, who acted
as one of its nine initial sponsors.
In fact, Onicescu was not only an academic and a scientist. He was
a great personality of Romanian culture and, especially in the
inter-war period, he played an important part in the cultural,
scientific and social activities of his country. In that period
Onicescu co-edited such periodicals as {\it Natura (Nature)} and
{\it Ideea european$\breve{a}$ (European Idea)}, where he
contributed scores of papers on most various scientific, cultural
and philosophical matters. He wrote frequently in newspapers on
social, economic, demographic, and political issues - he even
belonged for a while on an independent basis to the Chamber of
Deputies of Romania - and took an active part in the organization or
reorganization of several social, financial, teaching, and
scientific institutions. The last group includes the Romanian
Society of Sciences, where Onicescu was secretary general for many
years and then president. He also presided over the Central
Commission for the 1941 general population census in Romania. In
1938, as recognition of his many achievements, Onicescu was elected
corresponding member of the Romanian Academy. He lost this rank in
1948, when the institution was reorganized, and it was only in 1965
that the injustice was repaired and Onicescu was made a full member
of the Romanian Academy.
In more recent times, Onicescu's involvement in cultural and social
matters manifested itself by his intensive participation in the
activities of the Romanian Committee for the History and Philosophy
of Sciences and above all by the organization and leadership of a
Seminar on the applications of statistical and mathematical methods
to economics at the Central Board of Statistics in Bucharest.
Opened in January 1965, this seminar met regularly every week
except for holidays. After some 450 sessions, it only ended with
the physical disappearance of its initiator in 1983. Actually, in
his last 20 years Onicescu took a keen interest in economics. In
this context he was led to reconsider Gini's 1912 homogeneity
coefficient $1-S$ under the name of {\it information energy} and to
strongly advocate its use in various fields and as a basis for the
constructing of the so-called {\it information statistics}; see
[4], [5], [8].
Onicescu received international recognition for his mathematical
researches. Elected as an ordinary member of the International
Statistical Institute in 1935, he became an honorary member in
1982. Onicescu was also a member of the Academy of Sciences of
Turin (since 1976).
Onicescu's mathematical career eludes normal appreciation and
assessment. Fortunately, he provided a marvellous characterization
of this scientific endeavour in a speech delivered at the Romanian
Academy on the occasion of the celebration of his 75th birthday as
follows:
\begin{quote}
``I am not first of all a mathematician, by no means a probabilist
as most agree, not even a mechancian as some do not want to
consider me. I regard myself as a researcher of human actions,
either social or enonomic, and natural phenomena, who used
mathematical tools, preferably probabilistic or mechanical, who all
his life strove to assimilate as much mathematics as he could for
using it in his researches. I cultivated probability as a science
of measurement of random events and processes. I cultivated
mechanics as a support or a model of any science of natural motion.
In this long and difficult way I met geometry, algebra, and
analysis, sometimes topology, and I did not hesitate to take up the
problems raised. It was my chance that at any important moments of
my scientific or social enterprises I enjoyed ideas, and enthusiasm
to materialize my projects that become common to all of us".
[Tanslation from the Romanian of {\it An. Acad. R.S. Rom\^{a}nia}
(4) {\bf 18}(1986), p.295.]
\end{quote}
Fully in accordance with these words, the emphasis in Onicescu's
mathematical work is on concepts, motivation and applicability
rather than on technicalities.
There are two distinct phases in Onicescu's work in probability. In
a first phase (up to 1958) he collaborated intensively with his
first doctoral student Gheorghe Mihoc (1906-1981). Onicescu and
Mihoc introduced and studied the concept of a chain with complete
connections (see [2]), did an exhaustive study of the asymptotic
behaviour of partial sums associated with finite Markov chains by
using the method of characteristic functions and wrote several
books on probability and mathematical statistics. This joint work
laid down the basis of the Romanian school of probability theory.
Mention should also be made here of Onecescu and Mihoc's
co-founding in 1955 of the Bra\c{s}ov Conferences on Probability
Theory, which clearly put this school into the limelight. This
phases of Onicescu's work in probability is very well described in
Mihoc's essay [3]; also in Onicescu's obituary notice on Mihoc
[7].
In the second phase (after 1958), Onicescu's main achievement in
probability was the elaboration of a new framework of probability
theory, which replaces the classical event space, viewed as a point
set equipped with a $\sigma$-field of subsets (Kolmogorov's
axiomatization), by an abstract Boolean $\sigma$-algebra, thereby
avoiding the consideration of the 'elementary event'. The new
system based on the concepts of a sum function, which is an
analogue of the indefinite integral, and a separator, which is an
analogue of the family of sets $\{\omega: f(\omega) <
\alpha\}_{\alpha}$ where $\alpha$ runs over the reals and $f$ is a
random variable (in the Kolmogorov system). The monograph [4]
aimed at clarifying the part the new theory could play in the
foundations of probability theory.
A fairly complete list of publications of Onicescu containing 222
papers and 32 books can be found in [1].
Onicescu died in Bucharest on 19th August 1983, the eve of his 91st
birthday, after a short illness. He was a man with a great deal of
charm and wit, who enjoyed an exceptional family life. This is
apparent from the two volumes of memoirs [6] he was able to
complete.
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\begin{thebibliography}{3}
\bibitem{1}
[1] M. Iosifescu, (1986). Obituary notice : Octav Onicescu, 1892-1983.
{\it International Statistical Review}, {\bf 54}, 97-108.
\bibitem{2}
[2] M. Iosifescu \& \c{S}. Grigorescu, (1990). {\it Dependence with
Complete Connections and Its Applications}. Cambridge Univ. Press,
Cambridge.
\bibitem{3}
[3] G. Mihoc, (1982). A life for probability. In J. Gani (Ed.)
{\it The Making of Statisticians}, pp. 22-37. Springer, New York.
\bibitem{4}
[4] O. Onicescu, (1969). {\it The Principles of Probability Theory}.
Publishing House of the Romanian Academy, Bucharest.
(Romanian).
\bibitem{5}
[5] O. Onicescu, (1972). Principles d'une Statistique informationnelle.
{\it Metron}, {\bf 30}, 3-19.
\bibitem{6}
[6] O. Onicescu, (1982 \& 1984). {\it Memoirs} Vols.1 \& 2. Scientific and
Encyclodpedic Publishing House, Bucharest.
(Romanian).
\bibitem{7}
[7] O. Onicescu, (1993). Notice n\'ecrologique: Gheorghe Mihoc, 1906-1981.
{\it International Statistical Review}, {\bf 51}, 323-327.
\bibitem{8}
[8] O. Onicescu and M.C. Botez, (1985). {\it Uncertainty and Economic
Modelling:
Information Econometrics}. Scientific and Encyclopedic Publishing
House, Bucharest. (Romanian).
\hfill{ Marius Iosifescu}
\end{thebibliography}
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